Oscillograph and cathode-ray tube therefor



H T Y M S N c OSCILLOGRAPH AND TO CATHODE-RAY TUBE THEREFOR Filed Aug. 19, 1947 Attorney Patented May 30, 1950 OSCILLOGRAPH AND CATHODE-RAY TUBE THEREFOR Charles Norman Smyth, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application August 19, 1917, Serial No. 769,553 In Great Britain June 1, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires June 1, 1960 2 Claims.

This invention relates to circular trace oscillographs and to cathode ray tubes primarily intended for use therein.

Circular trace oscillographs are used for a number of purposes, circular trace being provided by two separate deflecting arrangements (either electric or magnetic) arranged at right angles to each other and symmetrically placed with respect to the axis of the cathode ray tube and fed with sinusoidal currents or voltages of equal frequency but 90 out of phase with each other. If it is now proposed to use this circular trace as abscissae and then to produce radial deflections as ordinates, these radial deflections will in general contain very much higher frequency components than those present in the circular trace currents, for example suppose a circular trace has a periodicity of about 2000 R.P.S. and the radial deflections are to have a width of say 1 degree, the frequencies present in the radial deflection will correspond to 720,000 and its higher harmonics.

On a, large oscillograph working at higher voltages it would be very difficult to design a deflecting system which would provide a circular trace and at the same time have sufficiently good frequency response to handle the frequencies required for radial deflections of the order mentioned.

It is proposed, therefore, to provide such oscillographs with two separate deflecting systemsone of conventional type (either magnetic or electric) providing the circular trace and another one of either magnetic or electric type for providing the high frequency radial deflections. As is well known a deflecting system for a cathode ray tube normally comprises either two pairs of coils with their axes at right angles to each other and to the tube axis or two pairs of electrostatic deflecting plates, the pairs being at right angles to each other and lying in planes parallel to the tube axis.

It will be clear that it is necessary to interconnect in some way the two deflecting systems otherwise the one producing the ordinates will not produce lines which are normal to the circular trace at every angle. It is further proposed, therefore, to feed the auxiliary deflecting system through two amplifiers whose conductances are controlled by the outputs from the circular trace amplifiers.

Fig. 1 of the drawings shows in schematic form the proposed circuit arrangement. The coils A are the main deflecting coils providing the circular trace; coils B are those for providing the radial deflection. Coils A are fed from the ampli- 2 fiers i and 2 and the coils B from the amplifiers 3 and 4.

Firstly to provide the circular trace a sine wave oscillator 5 oscillating at 2000 C.P.S. feeds into a phase-splitting device 0 from which two separate outputs go to amplifiers l and 2. These outputs diifer in phase by The amplifiers I and 2 then feed sinusoidal currents still differing in phase by 99 to the coils A and provide the circular trace.

The signal which it is desired to show on the oscillograph as a radial deflection is applied to terminal C and fed in parallel to the amplifiers 3 and d. It will then be passed on to the coils B1 through the amplifier 3 and B2 through the amplifier 4 depending upon the conductance of these amplifiers.

N ow the conductance of the amplifier 3 is controlled from the output of amplifier I via the lead I and the conductance of amplifier 4 is controlled from the output of amplifier 2 via the lead 8. Thus it can be seen the ratio of the currents in B1 and B2 will depend on the ratio of the conductance of the amplifiers 3 and 4, and these in their turn depend upon the outputs of the amplifiers l and 2. Thus the angle at which the radial deflection takes place will be definitely related to the position of the scanning spot at that particular moment and upon suitable adjustment of the connections of the coils, will be normal to all points of the circular trace.

It will be noted that the amplifiers 3 and 4 whose conductance has to be varied in accord with the outputs of amplifiers I and 2 must be capable of having at various parts of the cycle either positive or negative conductance. This difiiculty can be overcome by using a, cathode ray tube with a biassed or skew beam and passing permanent deflecting currents through the coils B1 and B2 to keep the initial position of the beam central.

Variation of the conductance of 3 and 4 will then cause deflections of the beam in either positive or negative directions while the conductance of 3 and 4 remains positive. This method is diflicult and not easy to apply.

Amplifiers with alternately positive and negative conductance can however, be constructed on a principle which will be clear from the embodiment shown in Fig. 2 of the drawings. Such an amplifier is therefore preferably used at 3 and 0 in Fig. 1. It will be assumed in describing Fig. 2 that the amplifier circuit is to constitute the amplifier 2 of Fig. 1.

In Fig. 2, V1 and V2 are two valves connected 3 as in a push-pull circuit, the output being taken from the transformer T2 and applied to deflector coils B1. The input signal at C is fed in parallel and in phase to the two grids G1 and G2 but the bias applied to the valves V1 and V2 through the grid leaks L1 and L2 varies sinusoidally and diiTers by 180 between the two valves. It is supplied from the transformer T which is fed from the amplifier I to Fig. 1 over conductor I. Thus it will be seen that during part of the cycle V1 is more strongly operative than V2 and during the other part of the cycle V2 is more strongly operative than V1. Thus the conductance of this amplifier will vary through positive and negative 7 values as the voltages applied to T vary through positive and negative values.

Other possible arrangements will now be appreciated constituting a circular trace oscillograph according to the invention and comprising a cathode ray tube with two beam-deflecting systems, each providing deflection in two directions at right angles, means for applying dephased sinusoidal voltages or currents to one deflecting system to set up a circular trace and means for applying voltages or currents including signal components to the other deflecting system for radial deflection of the beam.

It will also be clear that the cathode ray tube of the invention comprising two beam deflecting systems each providing deflection in two directions at right angles, and having difierent effective frequency ranges, has many applications in addition to its use as described.

What is claimed is:

1. Circular trace oscillograph comprising a cathode ray tube with two beam-deflecting systems, each providing deflection in two directions 7 at right angles, means for applying dephased sinusoidal waves to one deflecting system to set up a circular trace, second means for applying electrical energy including signal components to the other deflecting system, and third means for cyclically varying the relative amplitudes of the signal components to provide a radial deflection proportional to the signal components, said third means comprising two amplifiers through which the signal components are fed, the conductances of said amplifiers being respectively controlled by the dephased sinusoidal waves set up for circular deflection.

2. Circular trace oscillograph according to claim 1, wherein each amplifier comprises two valves connected to be fed in parallel with the signal waves and having a push-pull output to its associated pair of deflector elements, biassing connections being provided for the two valves wherebysinusoidal waves from. an amplifier feeding onepair of main deflector elements are applied in phase opposition to the respective valves to render them alternately effective to pass the signal waves.

CHARLES NORMAN SMYTH.

REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,121,359 Luck et al June 21, 1938 2,233,275 Wolfi Feb. 25, 1941 2,252,083 Luck Aug. 12, 1941 

